This invention relates to a manufacturing method for a spark plug installed in an internal combustion engine of an automotive vehicle or the like.
A conventional spark plug has a columnar center electrode insulated and held inside a metal housing and a ground electrode having one end being bonded to the housing, wherein the ground electrode is bent at its intermediate portion so that the other end of the ground electrode is opposed to a distal end surface of the center electrode.
A spacer is used for regulating a bending amount in a provisional bending step of the ground electrode, so that a spark gap is suppressed or regulated within a predetermined range at the end of the provisional bending step (refer to Japanese Patent Application Laid-open No. 2000-164320).
However, according to the manufacturing method disclosed in the above-described prior art document, the protruding amount of a distal end surface of the other end of the ground electrode is not constant.
In other words, the unevenness of the protruding amount increases. This is an ignition property deteriorating factor of the spark plug. In this specification, the “protruding amount” is an overhang of the distal end surface of the other end of the ground electrode with respect to the axial line of the center electrode in a direction perpendicular to the axial line of the center electrode.